It has been stated by Lucian in An Elite Meet and Greet! that when a Trainer wins their respective region's Conference Tournament, they can participate in the Champion League, fighting the four members of that region's Elite Four, and then possibly the Champion as well. It has also been shown that an Elite Four member can challenge the Champion and obtain the title from him or her in battle.

The Unova Elite Four first appeared in the Black & White chapter as Black cites them during his daily pledge. However, they haven't appeared to the main characters as a group yet. Besides Caitlin, who already appeared in the Platinum chapter, Grimsley meets Black, Shauntal meets White and Marshal meets both on different occasions.

In the Pokémon Zensho manga

The Kanto Elite Four members appeared in Indigo Plateau, where all of them were defeated by Satoshi, allowing him to face the Champion, Shigeru.

Trivia

In the Kanto-based games, every Elite Four member has at least one Pokémon not of their specialty type during the first battle.

The Kalos Elite Four members are the only ones that don't have higher level Pokémon in future rematches with them in any game.

Prior to Pokémon HeartGold and SoulSilver, the Elite Four typically progressed in level with their Pokémon in the games. The rematch teams in HeartGold and SoulSilver don't progress in level like in all previous games and even the pre-Kanto teams used by the same Elite Four. In Generations V and VI, all members of the Elite Four use Pokémon of the same levels, as they can be challenged in any order.

Also, Aaron's highest-leveled Pokémon, Drapion, and one of Bertha's Pokémon, Gliscor, match Kincaid's first and second Pokémon, respectively.

The Sinnoh Elite Four and Generation I Elite Four are the only ones in which each member has made an appearance in the anime.

In Generation V, all Elite Four members' type specialties have been used exactly twice in Elite Four of other regions. The Indigo Elite Four used all of them, spread in its two variations (with a Fighting-type specialist in both), the Hoenn Elite Four has Dark- and Ghost-type specialists, and the Sinnoh Elite Four has a Psychic-type specialist.

All of the Kalos Elite Four use two Pokémon introduced in Generation VI.

In Omega Ruby and Alpha Sapphire, the highest-leveled Pokemon of the female members of the Elite Four differ when rematched. This is because the Elite Four obtain Mega Stones for the rematch, but Dusknoir and Walrein (the highest-leveled Pokemon of Phoebe and Glacia, respectively) do not have Mega Evolutions.